Technical Field
The present disclosure relates to a dispensing apparatus that dispenses liquid samples.
Background Art
When analyzing liquid biological samples, the liquid sample is sucked into a nozzle, and then the liquid sample is discharged from the nozzle to a component that will hold the liquid sample. Examples of the component holding the liquid sample may include slide glass substrates, array elements, liquid containers, or micro plates. In order to precisely analyze the sample, it is necessary to precisely control the liquid volume of the sample to be discharged.
In DNA micro arrays, hundreds to tens of thousands of biological substances or chemical substances are aligned and fixed at high density on a slide glass substrate having a size of several square centimeters. The sample is analyzed by searching substances that interfere with the substance on the substrate, and by identifying signal patterns of the interfering substance. In order to improve measuring accuracy, it is important to dispense the sample by predetermined volumes precisely.
In order to always provide micro volume of the liquid sample at constant volume rate, typical dispensing apparatuses expose the sample from the tip of the nozzle by a very small volume to form at the nozzle tip a droplet having a very small diameter. This droplet is dispensed onto the dispense target surface.
Patent Literature 1 listed below describes a method for preventing variation of spot sizes that may occur due to contact status between the nozzle tip and the substrate. In Patent Literature 1: the distance between the nozzle and the dispense target surface is kept constant by a locating pin; the nozzle tip does not contact with the dispense target surface; a micro droplet containing proteins is held at the nozzle tip, and the droplet is contacted with the dispense target surface; and the sample is dispensed without contact using surface tension of the droplet.
If the quantitatively analyzed sample is a biological sample such as blood or urine, or when using expensive reagents in analysis, it is desirable to limit the amount of sample up to several micro liters, so that the amount of used reagent is limited. In a case of blood sample, it is difficult to acquire large amounts of the sample. Thus it is desirable if many items can be analyzed using small amount of the sample as small as possible. The amount of biological sample dispensed to one piece of liquid container is necessarily small. In current technologies, a sample volume for performing one analysis may be under 1 microliter. It is necessary to discharge such micro volume sample by a predetermined volume to the liquid container.
Patent Literature 2 listed below describes a method for controlling the sequence of discharge according to the liquid volume discharged to the liquid container. In Patent Literature 2, if the discharged volume is at or less than 5 micro liters, the tip of dispensing nozzle is pressed onto the bottom of the liquid container and then the sample is discharged, so that the sample discharged from the nozzle using the surface tension of the sample can smoothly move to the liquid container. If the discharged volume is more than 5 micro liters, in order to prevent from the peripheral of the nozzle tip being polluted by the discharged sample, the nozzle tip is positioned at several millimeters above the bottom of the liquid container and then the sample is discharged.